The cave located atLa MarcheLa-Roche-aux-F?es is a 64ft (19.5m)-long passage grave, which is 20ft (6m) wide and 13ft (4m) high. The purple-hued stones were mined about 3000BC in the forest at Theil-de-Bretagne - 2.5 miles (4km) to the south of Ess?; each one weighs several tonnes and the ensemble is thought to weigh around 500 tonnes. And that's how the structure got its name - since the stones were so heavy, it was thought that fairies brought them to the site. The dolmen is aligned with the sun's first rays at Winter Solstice (21 December).